Wireless backhaul networks are deployed to carry the traffic between a wireless access network and the core network. For example, as described in the above referenced related patent applications, a wireless backhaul network may comprise a plurality of hubs, each connected to the wired core network, via Ethernet. Each hub serves multiple Remote Backhaul Modules (RBMs), in a point-to-multipoint or point-to-point configuration, using a wireless channel Each RBM is deployed close to an access network base station, such as a small cell base station, and connected to the base station via a cable. The hubs are deployed at the locations where wired high capacity access to the core network is available, e.g. at a fiber point-of-presence.
In a wireless backhaul network, the term cluster refers to a number of RBMs and their respective serving hub. The performance of an RBM, e.g. such as throughput, is contingent upon its received carrier-to-interference-plus-noise ratio (CINR) and the amount of bandwidth allocated to this RBM given a selected carrier. The received signal strength of an RBM is determined by the transmit power of a serving hub and the path loss between the serving hub and the RBM. The received interference-plus-noise level of an RBM is determined by the transmit powers of all interfering hubs and path losses between interfering hubs and the RBM. An RBM is affected by an interfering hub when a desired signal and an interfering signal are transmitted over the same carrier frequency.
In frequency reuse of 1, multi-sector deployment, there are two main types of interference, namely intra-cell interference and inter-cell interference. The problem of resource allocation and scheduling has been extensively researched in multiple dimensions, e.g., time, frequency and space. Fractional frequency reuse techniques coupled with power management have been researched and many methods have been proposed in the literature to obtain a good performance trade-off. However, the system performance is far from an interference-free performance upper bound in terms of capacity and reliability.
In typical wireless backhaul networks, hubs and RBMs are deployed at fixed locations, and hubs are located at elevated locations with sufficient height above obstacles or other environmental clutter. For example, in an urban area, hubs may be positioned on a tall building or a rooftop, above the clutter. Each RBM is typically co-located with an access network base station, e.g. for a small cell base station, on a utility pole, a sidewall of a building or other location below the roofline. Thus, typically there is not a direct line of sight (LOS) between an RBM and a hub.
For example, each site or cell may comprise three sectors, i.e. three hub modules with directional antenna, with each hub module serving a cluster of up to four RBMs. The above referenced related U.S. patent application Ser. No. 14/129,150, describes a method and apparatus for determining network clusters for wireless backhaul networks, i.e., determining which RBMs are assigned to each serving hub to provide improved system performance.
For systems in which each hub module has multiple beams, proper hub-beam selection for each hub-RBM radio link can further improve system performance. Known methods for hub-beam selection include geographic location-based hub-beam selection. However, when a new RBM joins the network, such methods for selection for the new RBM may disrupt operation of other hubs and RBMs, i.e. cause inter-site or intra-site interference with other existing RBMs and hubs already in operation.
An object of the present invention is to provide an improved or alternative method and system for hub-beam selection in wireless networks and particularly for wireless backhaul solutions comprising fixed or stationary nodes with directional antennas, including small-cell non-line-of-sight (NLOS) wireless backhaul networks.